How to implement the factory method pattern in C++ correctly

Question

There\'s this one thing in C++ which has been making me feel uncomfortable for quite a long time, because I honestly don\'t know how to do it, even though it sounds simple:<

Answer 1

You can read a very good solution in: http://www.codeproject.com/Articles/363338/Factory-Pattern-in-Cplusplus

The best solution is on the "comments and discussions", see the "No need for static Create methods".

From this idea, I've done a factory. Note that I'm using Qt, but you can change QMap and QString for std equivalents.

#ifndef FACTORY_H
#define FACTORY_H

#include 
#include 

template 
class Factory
{
public:
    template 
    void registerType(QString name)
    {
        static_assert(std::is_base_of::value, "Factory::registerType doesn't accept this type because doesn't derive from base class");
        _createFuncs[name] = &createFunc;
    }

    T* create(QString name) {
        typename QMap::const_iterator it = _createFuncs.find(name);
        if (it != _createFuncs.end()) {
            return it.value()();
        }
        return nullptr;
    }

private:
    template 
    static T* createFunc()
    {
        return new TDerived();
    }

    typedef T* (*PCreateFunc)();
    QMap _createFuncs;
};

#endif // FACTORY_H

Sample usage:

Factory f;
f.registerType("Descendant1");
f.registerType("Descendant2");
Descendant1* d1 = static_cast(f.create("Descendant1"));
Descendant2* d2 = static_cast(f.create("Descendant2"));
BaseClass *b1 = f.create("Descendant1");
BaseClass *b2 = f.create("Descendant2");